The invention relates to a method of manufacturing a display device, in which a substrate is provided with groups of at least one pixel and a conductor pattern, and in which a semiconductor device for supplying drive voltages to the pixel is fixed to the substrate.
Examples of such active matrix display devices are the TFT-LCDs or AM-LCDs which are used in laptop computers and in organizers, but they also find an increasingly wider application in GSM telephones. Instead of LCDs, for example, (polymer) LED display devices can be used.
More generally, the invention relates to a method of manufacturing an electronic device, in which at least a substrate is provided with functional groups comprising at least a switching element, and in which a semiconductor device for supplying drive voltages to the switching element is fixed to the substrate.
The article xe2x80x9cFlexible Displays with Fully Integrated Electronicsxe2x80x9d, SID Int. Display Conf., September 2000, pp. 415 to 418, describes a process in which specifically formed semiconductor devices in a liquid suspension are passed across a substrate and reach correspondingly formed xe2x80x9caperturesxe2x80x9d or indentations in the substrate. The semiconductor devices are ICs which are manufactured by means of standard techniques. After the ICs have been provided, connections with pixels are established.
A problem occurring in this case is the fact that, for providing the ICs, considerable tolerances are to be taken into account. Not only must the semiconductor devices (ICs) glide, as it were, into the indentations but they also have a certain thickness (approximately 50 micrometers). Dependent on variations of thickness, certainly when not all ICs come from one and the same wafer, and variations on the surface of the substrate in the depth of the xe2x80x9caperturesxe2x80x9d or indentations, a variation will occur in the thickness of the electro-optical layer provided on the substrate, which thickness may amount to several micrometers. Notably when thickness-sensitive effects such as, for example, the (S)TN effect are used, this leads to unwanted discoloration and non-uniform switching behavior.
Inaccuracies during placement of the ICs must also be taken into account. When an IC xe2x80x9cglides into the indentationsxe2x80x9d, it may find its ultimate destination at an arbitrary location within this indentation. Consequently, the indentations occupy a much larger space than the semiconductor devices (ICs), which, notably in transparent display devices, is at the expense of the aperture. To be able to satisfactorily contact the ICs in the case of this inaccurate placement, these ICs must be provided with large contact surfaces, which is at the expense of IC surface area and renders the technology shown very expensive.
A further problem is the variation of the thickness of the semiconductor devices (ICs), related to the depth variation of the indentations so that local thickness variations occur in the ultimate surface area (the common surface area of the substrate). Conductor tracks extending in the device shown across the embedded semiconductor devices (ICs), thereby run a great risk of breakage.
To this end, a semiconductor substrate according to the invention is provided with a plurality of semiconductor devices whose surfaces have electric connection contacts, the semiconductor devices being mutually separated in a surface region of the semiconductor substrate and the electric connection contacts being coupled to the conductor pattern (in an electrically conducting manner) whereafter the semiconductor devices are separated from the semiconductor substrate.
Since the semiconductor devices (ICs) are similarly situated with respect to each other as on the semiconductor substrate during their fixation to the substrate, the ICs are provided at a very accurate pitch. This may be a constant pitch in one direction, such as in matrix-shaped configurations of the pixels. The pitch may alternatively be variable.
Moreover, due to this method of fixation, only parts of the surface area of the semiconductor substrate in which the active elements are realized can be provided on the substrate of the display device. Since these parts have a negligible thickness (less than 1 micrometer), said thickness-sensitive effects do not occur. Even the presence of a spacer at the location of an IC does not have any influence or hardly has any influence on the effective thickness of the liquid layer and hence on the operation of the display device, certainly when spacers with an elastic envelope are chosen.
A further advantage is that the ICs can now comprise drive electronics at the location of the pixels. This provides great freedom of design.
The semiconductor devices are separated, for example, by means of an etching treatment in a surface area of the semiconductor substrate. In an alternative method, the semiconductor devices are provided in a semiconductor layer on an insulating layer (SOI technology) and separated by means of an etching treatment in this semiconductor layer having a thickness of typically 0.2 micrometer. The result is that these semiconductor devices in the finished display device have a negligible thickness (less than 1 micrometer) as compared with the effective thickness of the liquid layer, so that said thickness-sensitive effects do not occur, not even in the presence of a spacer at the location of an IC. Moreover, the ICs are now placed with great accuracy and without taking extra precautions. The contact surfaces may now be considerably smaller, which occupies less IC surface.
These and other aspects of the invention are apparent from and will be elucidated with reference to the embodiments described hereinafter.